Here is an interesting youtube clip of a musician playing and discussing the features of carnyxes/carnacyes.
https://www.youtube.com/watch?v=lVFGT2NX-YQ
Also worth a look at this site (http://www.nms.ac.uk/explore/stories/scottish-history-and-archaeology/deskford-carnyx/) (it is linked from the YouTube page, but you have to hunt for it a bit), as it has another short video about the guy who made the instruments.
Not sure about the creation of the mouthpieces using an electric milling machine, as I'm pretty certain the ancients didn't have those, but interesting all the same. Perhaps still more interesting if someone had made it clear if the mouthpieces are based on archaeological examples, or were simply a modern interpretation based on the needs of wind instruments nowadays (given that could affect the range of sounds available).